A = [5 6 0 0 0
    1 5 6 0 0
    0 1 5 6 0
    0 0 1 5 6
    0 0 0 1 5];
B = [1 0 0 0 1]';
R_A = rank(A) % 求秩
format short
X = A\B % 求解
